It was good but something was missing

Yes, this is me the downer again.
I liked this book and the parts I enjoyed the most involved Megan and David together talking, working as a team, learning about each other. Those where the moments where the story really picked up big time and I felt the author was really engaged in those moments but I felt that rest of the plot really stall and we sort of got this in between book which kind of sucks.
I still like this series, I still think is really good and kind of original but we are kind of losing momentum. I will keep reading because Megan is freaking awesome and David is really funny but I am not as invested in the storyline as I once was.